Gerrit 3.12 cluster: Owner resolves to _account_id: 0 (“Name of user not set”) for all imported changes after migration

[Алия Моисеева]

Setup
Source: Gerrit 3.12 now (the issue also existed when the source was 3.10).
Target: new Gerrit 3.12 multi-node cluster. Bare repos on shared CephFS (/mnt/gerrit/git). Indexes & caches are local per node.
Replication: pull-replication from the source.
All-Users.git and All-Projects.git are present.

Symptom
In UI, Owner shows as “Name of user not set” for every existing change (snapshot2).

gerrit query --format=JSON --current-patch-set change:<N> → owner._account_id = 0 (while author/uploader resolve fine).

When only a single node was running, Owners resolved correctly. After bringing other nodes online, Owner disappeared for all existing changes. Since then, even if I stop the extra nodes and reindex, Owners do not come back.

New changes created directly on the cluster (not replicated) show Owner correctly.

On the cluster, /plugins/gitiles/All-Users renders “Empty repository” (snapshot 1). However, direct links to refs/users/* and refs/meta/* work and show fresh objects. On the source, /plugins/gitiles/All-Users lists refs normally. Other projects render fine.

What we already verified / tried:

1. gerrit.serverId is identical on all cluster nodes; gerrit.importedServerId is set to the source’s serverId. Also set index.cacheQueryResultsByChangeNum = false.
2. Multiple offline reindex rounds (accounts, changes, also tried projects/groups) + flush-caches --all. Before reindexing we deleted disk caches and local index dirs. Indices/caches are not on CephFS.
3. Explicit meta pull: git fetch +refs/changes/*:refs/changes/* from source to cluster repos → no change.
4. All-Users.git: added externalId = imported:<aid>@<sourceServerId> in refs/meta/external-ids for all local account IDs (1:1), then offline reindexed accounts and changes → still no Owner.

With correct serverId + importedServerId, healthy All-Users.git, non-shallow repos, caches cleared, and offline reindexing done, what else could cause Owner to resolve to _account_id: 0 for all imported changes?

Any known 3.12 issues around Owner resolution after migrations (patches/workarounds)?

Thanks in advance — happy to get your answer.

Best Regards,
Aliia